1. Field of the Invention
This invention relates to a camera image shake detecting apparatus for detecting an image shake by using the output signal from an image sensor provided to detect a camera focus.
2. Related Background Art
An image shake detecting apparatus for detecting an image shake by using the image signal of an object for photographing generated by a photoelectric converter of a focus detecting apparatus has been known (for example, see Japanese Patent Laid-Open No. 60-166911).
FIGS. 4A to 4C are views showing a state of detecting a focus by a conventional focus detecting apparatus. FIGS. 5A to 5C are views typically showing an image signal of an object for photographing to be detected by a photoelectric converter (image sensor) of the focus detecting apparatus. The conventional focus detecting apparatus will be described referring to FIGS. 4A to 5C.
The images of an object for photographing generated by light flux, which has passed through two different pupil areas of a photographing lens 1, are formed on two photoelectric converters 3a and 3b consisting of n p'cs of light receiving elements each through reimage forming lenses 2a and 2b to obtain a pair of image signals Fa and Fb of the object for photographing, shown in FIGS. 5A to 5C, corresponding to the light intensity distribution of the object image by photoelectrically converting by the photoelectric converters 3a and 3b.
FIG. 4A shows a focused state in which the image of the object obtained by the photographing lens 1 is formed on a predetermined focus surface 4 conjugate to the film surface. FIG. 4B shows a so-called "front focus state" in which the image is formed in front of the predetermined focus surface 4. FIG. 4C shows a so-called "rear focus state" in which the image is formed behind the predetermined focus surface 4.
During focusing as shown in FIG. 4A, a pair of images of the oject are formed at the same position on the photoelectric converters 3a and 3b, and an amount of relative displacement d (hereinafter called an "amount of relative displacement d for detecting the focus", and this is distinguished from an amount of relative displacement d' for detecting the image shake as mentioned later) between two image signals Fa and Fb of the object as shown in FIG. 5A is 0.
On the other hand, in the front focus state shown in FIG. 4B, a pair of images of the object on the photoelectric converters 3a and 3b are displaced by d1a and d1b respectively, whereby image signals Fa and Fb of the object are displaced by an amount of relative displacement d1 for detecting the focus corresponding to a sum (d1a+d1b) of displacements of each object image as shown in FIG. 5B.
Similarly, in the rear focus state shown in FIG. 4C, a pair of images of the object on the photoelectric converters 3a and 3b are displaced by d2a and d2b respectively, whereby image signals Fa and Fb of the object are displaced by an amount of relative displacement d2 for detecting the focus corresponding to a sum (d2a+d2b) of displacements of each object image as shown in FIG. 5C.
The focus detecting apparatus thus detects the focus detecting state of the photographing lens 1 by detecting the amount of relative displacement d for detecting the focus for a pair of image signals Fa and Fb of the object.
Then a method for calculating an amount of relative displacement d for detecting the focus will be described.
Assuming data for a pair of image signals Fa and Fb of the object obtained from the photoelectric converters 3a and 3b to be ap and bp (p=1 to n) respectively, the amount of correlation C (L) is obtained by correlation calculation shown in equation (1). ##EQU1## where L is an integral number, and is an amount of relative displacement of a pair of image signals of the object in which a pitch of the light receiving element is used as units. Also, a range of parameter i is appropriately determined in accordance with the amount of displacement L and the number of light receiving element n.
The calculation result of equation (1) is that an amount of correlation C (L) is minimal at an amount of displacement L=kj with high correlation data.
Then using the three-point interpolation technique in equation (2), a minimum value C (L) min=C (d) for a continuous amount of correlation is obtained. ##EQU2##
The amount of defocus DEF in proportion to a distance between the image surface of the object on the photographing lens 1 and the predetermined focus surface conjugate to the film surface can be obtained from the amount of relative displacement d for detecting the focus obtained from the equation (2) by using equation (3). EQU DEF=KX.multidot.PY.multidot.d (3)
where PY is a pitch in the arranging direction of the light receiving elements constituting each light receiving portion of the photoelectric converters 3a and 3b. KX is a coefficient which is determined by the construction of the focus detecting optical system.
By obtaining an amount of driving for the photographing lens 1 from this amount of defocus DEF, the photographing lens 1 is driven by the lens driving portion for focusing.
Then a conventional image shake detecting apparatus will be described.
When the focus is detected again and it is judged to be in a focused state after the photographing lens 1 is driven for focusing on the basis of the amount of defocus DEF calculated by the focus detecting device as mentioned above, the image signal of the object Fa is gathered twice at a time interval from one side of the photoelectric converter for detecting the focus, for example, 3a. At this time, the image signal Fb of the object from the photoelectric converter 3b may be used.
Assuming the object image signal for the last time of the photoelectric converter 3a to be Fa' and the object image signal for this time to be Fa respectively as shown in FIG. 6, the amount of relative displacement between these object image signals for the last time and this time Fa' and Fa is obtained by using the above-mentioned equations (1) and (2).
Although the object image signals Fa' and Fa gathered after focusing should be essentially at the same position, an amount of relative displacement in proportion to the amount of shake, that is, an amount of relative displacement d' for detecting the image shake as shown in FIG. 6 is detected should there be an image shake.
A conventional image shake detecting apparatus gives a warning about shake or changes the shutter speed not to cause any image shake in accordance with the amount of relative displacement d' for detecting the image shake.
In the conventional image shake detecting apparatus, however, since a shake is detected by detecting the temporal displacement in the object image signal of one side of the photoelectric converter for detecting the focus, the state of focusing changes, and this causes a change in the position of the object image, causing an error in the shake detection when the photographing lens is driven while the shake is being detected. Therefore, the shake should be always detected while the lens is not driven, that is, after focusing is performed and driving of the lens is stopped. For this reason, there is a problem that a shake cannot be detected while the lens is being driven for focusing.
Especially, in so-called "chase driving mode", which detects the focus by chasing a moving object for photographing and always drives the photographing lens on the basis of the focus detecting result, it becomes impossible to detect any image shake because the process enters a focused state or a nonfocused state.
Also in so-called "single mode" or "one shot servo mode", in which the lens is not driven after focusing, "mirror up" and exposure cannot be performed immediately after focusing because an image shake has to be detected after focusing, and the response during shutter release is inferior.
In a focus detecting device for calculating the amount of defocus of a photographing optical system by forming a pair of an image of the object for photographing on photoelectric converting means from a pair of light flux passing through the photographing optical system by means of the so-called "pupil division system" focus detecting optical system, obtaining the object image signal by photoelectrically converting this object image by the photoelectric converting means, and performing a predetermined calculation for this object image signal, an image shake detecting apparatus for detecting an image shake by using the object image signal generated by the photoelectric converting means in the focus detecting device has been proposed in, for example, Japanese Patent Laid-Open No. 166911.
In the image shake detection, an amount of relative displacement d for one side of image signals (Fa, Fa' or Fb, Fb') which are temporally different as shown in FIGS. 18A and 18B, is obtained through the difference type correlating algorithm of the same equations (1) and (2) as the above-mentioned focus detecting calculation by using photoelectric converting means 3 for detecting the focus after judging it as focused due to the above-mentioned focus detection.
For example, assuming the data of the object image signals Fa and Fa' to be a(p) and e(p) (however p=1 to n), an amount of correlation C (L) is obtained through the difference type correlating algorithm shown in equation (4) similar to equation (1). ##EQU3## where L in equation (4) is an integral number, and is an amount of relative displacement in which a pitch of light receiving element for a pair of light receiving element output data is used as an unit.
The calculation result of equation (4) is that an amount of correlation C (L) is minimal at an amount of shift L=kj with high correlation data. Then using the three-point interpolation technique in the same equation (5) as equation (2), an amount of relative displacement, which gives a minimum value C (L) min=C (d) for a continuous amount of correlation, is obtained. ##EQU4##
The amount of relative displacement d obtained from equation (5) is an amount of image shake Br, and a warning about shake has been given or the shutter speed has been changed not to cause the image shake in accordance with the amount of image shake Br.
In an image shake detecting apparatus using such a conventional pupil division system focus detecting device, there was a problem at issue that the image shake detection malfunctions when the output level for the object image signal varies at a different time. That is, when an image shake is detected for an object for photographing lighted by a light source, the brightness of which varies with time like a fluorescent lighting, the output level of the object image signal occurring at a different time differs as shown in FIGS. 19A and 19B even if the charge accumulation time of the photoelectric converting means is the same.
In this case, there is a relationship shown in equation (6) between one side of the object image signals Fa=G(x) and Fa'=H(x) (x represents the position of the light receiving portion of the photoelectric converting means in the arranging direction) at times T=T1 and T=T2. EQU H (x)=M.times.G (x+Br) (6)
In equation (6), M is a coefficient showing the output fluctuation, and M is M=1 when there is no fluctuations. Also Br is an amount of image shake between time T1 and time T2. When the coefficient M=1, a minimum value for the amount of correlation C (L) obtained through the difference type algorithm becomes almost zero as shown in FIG. 13A, and the amount of image shake Br can be correctly obtained by using the three-point interpolation technique in equation (5). When the coefficient M is not 1, a minimum value for the amount of relative correlation C (L) obtained through the difference type algorithm shown in equation (4) greatly rises from zero as shown in FIG. 13B, and the amount of image shake obtained by the three-point interpolation technique in equation (5) has an error against the correct amount of image shake Br.